Consider the reaction $H_2SO_{3(aq)} + Sn^{4+}_{(aq)} + H_2O_{(l)} \to Sn^{2+}_{(aq)} + HSO_4^-(aq) + 3H^{+}_{(aq)}$. Which of the following statements is correct?

• A
  $Sn^{4+}$ is the oxidizing agent because it undergoes oxidation
• B
  $Sn^{4+}$ is the reducing agent because it undergoes oxidation
• C
  $H_2SO_3$ is the reducing agent because it undergoes oxidation
• D
  $H_2SO_3$ is the reducing agent because it undergoes reduction